With this circuit it is possible to demonstrate the working principle of an optocoupler. The LEDD transmits the 60 Hz snoring from the power grid to an LDR (R4). The amplified snoring is reproduced in a headphone of 500-ohm or more. A piezoelectric capsule can be used in parallel with a 4k7 resistor. The transformer has a secondary of 6 V x 100 mA or more and R1 can be 4k7. It is convenient to connect a 1k resistor in series with it. R2 can be 470k and power can be supplied with 6V for both batteries.
